Polymethacrylate ester/polysiloxane block copolymers are known. Their synthesis, however, creates considerable problems. The state of the art is given in the following publications:
In the German patent 21 64 469 and the U.S. Pat. No. 3,663,650, the reaction of cyclopolysiloxanes, such as hexamethyltrisiloxane, with methacrylate in the presence of an aromatic lithium carbanion initiator, such as dilithium benzophenone, for the purpose of synthesizing such compounds, is disclosed.
According to the Polym. Bull. (Berlin), 15 (2), 107-122, ABA block copolymers are synthesized by the reaction of poly(methyl methacrylate), controlled with mercaptopropylalkyl-alkoxysilanes, with hydroxy-functional polysiloxanes.
In Polym. Prepr. (Am. Chem. Soc. Div. Polym. Chem.), 29 (1), 148-149, a method is described for the synthesis of AB block copolymers on the basis of polydimethylsiloxane and poly(methyl methacrylate) by anionic polymerization and group-transfer polymerization.
Mason, J. P. et al. (Polym. Prepr., Am. Chem. Soc. Div. Polym. Chem. 30 (1), 259) describe the addition reaction between hexamethylcyclotrisiloxane and anionic "living" poly(methyl methacrylate), an AB block copolymer being obtained.
In the journal named, the same authors describe the synthesis of poly(methyl methacrylate)-polydimethylsiloxane block copolymers with a star structure or of the ABA type by the addition reaction of hexamethylcyclotrisiloxane and monohydroxy-terminated poly(methyl methacrylate) and subsequent termination with alkyl chlorosilane.
It is a disadvantage of the syntheses described that either they are carried out by anionic methods, which require the use of monomers of high purity and demand the implementation of the reaction at temperatures below 0.degree. C. or the linking of the segments takes place over Si--O--C bonds, which are susceptible to hydrolysis. Because of the high sensitivity of the alkoxysilyl group of the chain transfer reagent used, the synthesis method, named in second place, also has disadvantages, since moisture must be excluded carefully during the reaction.
Recently, functionalized polyacrylate esters, which can be obtained by the transesterification reaction between alkyl polyacrylate esters (alkyl groups with 1 to 8 carbon atoms) and special alcohols, which generally have functional groups, have frequently been described, for example, in the German patents 38 42 201 and 38 42 202, as well as in the German Offenlegungsschriften 39 06 702, 40 06 093, 41 23 478, 42 02 187 and 42 24 412.
Compared to the analogous copolymerization products, the transesterification products have significant advantages such as an essentially more uniform molecular weight distribution. They are largely free of monomers. It is only by a transesterification method that it is possible to synthesize polyacrylate esters, the alcoholic ester component of which has olefinic double bonds, without forming higher molecular weight by-products. For example, it is readily possible to transesterify polyacrylate esters with oleyl alcohol and, at the same time, with other compounds having hydroxyl groups.
For these transesterification methods, the transesterification generally proceeds to the extent of about 70%, products being obtained with an, at least, approximate random distribution of the alcohols, introduced by the transesterification along the polymer chain.
These transesterification methods cannot readily be carried out with the corresponding alkyl polymethacrylate esters.
Admittedly, it is known from Chemical Abstracts 98 (No. 8, 54652f) that polymethacrylate esters can be reacted with a large excess of diethylaminoethanol at temperatures in excess of 150.degree. C. in the presence of titanates as catalysts. By means of this reaction, polymers are obtained, in which a portion of the ester groups has been transesterified with diethylaminoethanol. At this temperature, however, relatively non-uniform products are obtained and thermal decomposition products cannot be avoided.
It was therefore surprising that it is possible, in a relatively simple manner and without forming unwanted by-products, to synthesize polymethacrylate ester/polysiloxane block copolymers by the transesterification of polymethacrylate esters with hydroxy-functional polysiloxanes and, with that, to obtain novel copolymers, which can be expected to have special properties and thus are of special interest from an application point of view.